Maxillaria tenuifolia 'Yamada's Yellow - Looking sick

[iLoveOrchids101]

Hi, I bought two Maxillaria tenuifolia 'Yamada's Yellow from Carmela orchids last fall. They were doing fine with weekly watering schedule. During winter I slowed it down to twice a week. For last month+ they are looking little sick...darkening of the bulbs and lost few leaves. Hoping to get some guidance to understand what's going on with these orchids and how can I recover them. Thank you.